1. Field of the Invention
The present invention relates to the separation of vital wheat gluten and starch and, more particularly, to a wet process for fractionating vital wheat gluten, starch, and bran-germ from the whole wheat kernel with minimum damage to the frictional, chemical and biological characteristics of the wheat kernel components.
2. Description of the Prior Art
The commercial production of vital wheat gluten and the separation of starch therefrom has been accomplished in the past using wheat flour or second clears (a small fraction of the flour stream) as the starting material by the "dough ball" process and modifications thereof, which processes essentially separate the wheat starch from the gluten protein. In one process, the gluten is maintained as a single coherent mass and the starch is washed out of a flour and water dough. Another process disperses the dough in water and the recovers the gluten particles on a screen. Variations of the basic dough ball process utilizing wheat flour account for a major part of the vital gluten produced commercially today. Until recently, no known gluten production process employed the whole wheat kernel as the starting material. This way probably because production of vital wheat gluten is a comparatively recent innovation which developed from starch recovery processes. Early starch recovery processes utilized the whole wheat kernel but could not be converted to gluten production because the process conditions were too harsh and destroyed or devitalized the gluten. On the other hand, dough ball or batter processing from wheat flour was relatively simple because the bran and the germ had been substantially removed in the milling process. In addition, high ash second clears worked well in the dough ball process and were available at attractive prices as a by-product of the flour milling industry. Consequently, wheat gluten processing had been flour oriented for decades and no need had apparently existed to motivate the development of a process starting from the whole wheat kernel. However, improvements in milling techniques coupled with a drastic decline in the number of operative flour mills has led to current shortages of and higher prices for clears. As a result, millions of pounds of vital wheat gluten are imported by the United States each year to meet demands domestic producers cannot fill.
Processes for vital wheat gluten-starch separation and gluten recovery which utilize the whole wheat kernel as the starting material are taught in U.S. Pat. No. 3,891,613 and U.S. Pat. No. 3,979,375. According to these processes the whole wheat kernel is tempered in water and impact milled or flaked. The resulting particles or flakes are thereafter hydrated to saturation to form a thick, dough-like mass and are mechanically worked in the presence of water to wash the wheat kernel components from the gluten. Complete dough hydration as a preliminary to fractionating, as taught in these patents, has always been considered an essential element in the effective separation and recovery of high quality wheat components in high yields.
Recently, it has been suggested that fractionation can be accomplished without need to first form a hydrated dough. In U.S. Pat. No. 3,951,938 the well known Fesca process for starch/gluten separation has been supplemented by a protein purification process to permit the recovery of a vital gluten fraction containing at least 80% protein on a dry basis. This patent, which uses wheat flour (not the whole wheat kernel) as the starting material, discloses mixing one part wheat flour with 1.2-2.0 parts water to form a suspension of flour in water, homogenizing the suspension by agitation in a pin mill, centrifuging the homogenized suspension to separate a heavy starch fraction from a light protein fraction, maintaining the protein fraction in a quiescent state for a time sufficient for the gluten therein to begin to hydrate and to begin to agglomerate into thread-like gluten formations, diluting the protein fraction with at least an equal amount of water, agitating the diluted fraction in a pin mill to completely hydrate and agglomerate the gluten and filtering the gluten agglomerates from the balance of the protein fraction. It has been found, however, that the starch and protein fractions recovered by this process do not evidence the very high quality or purity of the fractions recovered from hydrated dough processing and specifically from processes such as those taught in U.S. Pat. Nos. 3,891,613 and 3,979,375. The recovered starch fraction contains unseparated protein as an undesirable impurity and the gluten fraction contains unseparated starch as an undesirable impurity. Moreover, the recovered gluten product, although high in protein content, is not as high in vitality as gluten recovered from the hydrated dough fractionation processes of U.S. Pat. Nos. 3,891,613 and 3,979,375. This is probably due to the high shear forces employed during purification of the gluten using a pin mill. Finally, the process of U.S. Pat. No. 3,951,938 would be largely ineffective using the whole wheat kernel as a starting material since it provides no means for dealing with the bran-germ particles which would contaminate the protein fraction and interfere with gluten agglomeration.